With a month to go until the UK votes in the referendum on the country's membership of the European Union, all the Sunday papers cover the competing arguments put forward by the Leave and Remain camps.

On the inside pages the four men, Sir Terry Leahy, Justin King, Marc Bolland and Sir Ian Cheshire, say that while they are not "advocates of scaremongering, it is just good business to understand the risks before reaching a conclusion in this complex debate".

Writing in the Sun on Sunday, Prime Minister David Cameron echoes the retailers' warning, citing Treasury analysis which he argues would show "the average cost of the weekly family shop for food and drink would rise by almost 3%, that's £120 a year".

The prime minister says costs would potentially rise in the event of "Brexit" due to a weaker pound, meaning imports would be more expensive. "Families across Britain can't afford to leave the EU," Mr Cameron concludes.

The Sunday Telegraph reports on secret government papers which it says shows some EU states - France among them - are delaying a free trade deal between the bloc and Latin American states. Fourteen out of the 28 EU members are "trying to limit the agreement because they fear farmers will suffer from the increased competition", the paper says.

It quotes leading Leave campaigner, Employment minister Priti Patel, as saying EU membership meant the UK was "tied to a sinking ship" and "powerless to reach our own trade deals". Missed trading deals was costing the economy "money, jobs and growth," she says.

Andrew Rawnsley in the Observer believes "In" has "won the most important argument - about the economy", but says the British people "can be contrary when the mood takes them" and warns Remainers that "elites exuding any impression of entitlement are not fashionable at the moment". "Any sense that the 'In' campaign already feels entitled to claim victory in this referendum risks being punished at the polling booth," he says.

In its editorial, the Sunday Express voices concern that the referendum debate "is based on wild claims and relies on seeking personalities and organisations to give respectability to one side or the other. It has become a game of one-upmanship".

The Sunday Times uses its leader column to say that voters "cannot distinguish between genuinely expert views and an establishment stitch-up". "People are not fools," the paper adds, "they know that our membership of the EU is a balance of advantage to disadvantage."

'Catastrophic' crash

Many of the papers analyse the release of automated communications data sent by the EgyptAir Airbus which crashed into the Mediterranean on Friday, killing all onboard.

The Sunday Mirror says fire was detected on EgyptAir flight MS804 "two minutes before 66 people died", adding that experts believe it was caused by a bomb. "The relatively short time between smoke warnings and the plane going into a terrible seven-mile plunge suggests something more catastrophic than a cigarette or electrical fire," says the paper.

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According to the Sunday People, the fire that brought the aircraft down "was so rapid and catastrophic that experts fear it may have been sparked by a terrorist device".

The Sunday Telegraph quotes an anonymous pilot, who flies the larger Airbus A330 for a European airline, saying he believed the data log "suggested that the windows in the right side of the cockpit were blown out by an explosion inside the aircraft".

Aviation safety specialist David Learmount is quoted in the Sunday Express saying the key question currently is how the fire started, whether that is an "ordinary electrical fire" or was "started deliberately with a small explosion or incendiary device".

The Mail on Sunday quotes Simon Hradecky of the website Aviation Herald, which released the automated Acars maintenance messages from the crashed jet. He says the airliner's oxygen supply could have been breached, causing the fire to spread more quickly, so that it "becomes catastrophic within three minutes".

According to the Sunday Times, the information sent by the jet's onboard computer "might help explain what happened, but not why" and examination of the wreckage "will be vital".

But it may be "weeks or even months" before investigators find the Airbus's black box data recorders, notes the Observer, adding that "part of the search area has a seabed with challenging geology, and few have forgotten the two-year search needed to find the same parts of an Air France flight that crashed into the Atlantic in 2009".

Eye-catching headlines

Schools bans whistle as too aggressive - it's not just the children who have to raise their hands to get attention, according to the Sunday Times, as whistles have been banned from a primary school in Milton Keynes because they could leave pupils "afraid of the noise". Staff must raise a hand in the air to mark the end of playground breaks, the paper adds.

Sun, sea and MoT - according to the Sun on Sunday, the world's most-remote island - Tristan da Cunha in the South Atlantic - is seeking a mechanic to look after its 125 cars. The paper says the British Overseas Territory has one three-mile-long road. The job "comes with a salary of £25,000 a year, and the chance to play golf on the volcanic isle and fish".

Veggies get 'steak' for sizzling BBQ - not content with creating vegetarian sausages that look (and sort of taste) like their meaty counterparts, the Sunday Mirror reports the herbivores among us will soon be able to buy a "steak-shaped cauliflower and mushroom slice" as peak barbecue season approaches. Such steaks are "popular in trendy restaurants", Tesco manager Alison Stokes says.

'Watch me Legooo!' says Jack the amputee tortoise on wheels - after an unfortunate incident involving a garden strimmer left Jack without a back leg, an inventive vet found a prosthetic made from a Lego wheel was the best way to get the tortoise mobile again, reports the Mail on Sunday.

'Populist revolt' in Austria

The possible election in Austria of a president from the far-right Freedom Party is scrutinised in several papers, with the Mail on Sunday's Ian Birrell describing Norbert Hofer as "a father of four who speaks softly, smiles often and walks with a stick following a paragliding accident". "He also packs a Glock pistol under his smart suit," Birrell adds.

He goes on to say "this Austrian politician is expected to send shockwaves around Europe" and his election "would mark an ominous advance in the growing populist revolt against traditional politics across the West".

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Mr Hofer's "nationalist appeal to put 'Austria first'" won him 35% of the vote in the first round of the presidential election, says Birrell. Austria, he adds, "shows how far-right protest parties from Scandinavia to Greece" are "riding waves of frustration with Brussels and conventional politics".

"There are fears [Mr] Hofer may use the instruments of the president's office... to dissolve the government and usher in a chancellor from his own party, which is currently leading in the polls," Oltermann writes.

"Hofer's rise reflects the boost the migration crisis is giving far-right forces across Europe," says the Sunday Times. More than 90,000 people, mostly Muslims - applied for asylum last year in Austria, the paper adds, which is equivalent to 1% of the country's population.

The paper adds that Mr Hofer would not be the first Austrian president to be "embroiled in controversy", relating how Kurt Waldheim - the former UN secretary general elected to the post in 1986 - "was revealed to have served as a young man in the Wehrmacht (armed forces) near the site of Nazi war crimes in the Balkans".

What the commentators say

Van Gaal gone

Louis van Gaal's imminent replacement as Manchester United manager by "special one" Jose Mourinho is widely written about after his team lifted the FA Cup for the twelfth time on Saturday.

"Dutchman LVG" is due to meet key Man Utd executives on Monday, reports the Sunday Mirror, "for talks to confirm that he is being replaced this summer by the former Chelsea boss". Van Gaal had hoped to work the final season his three-year contract, the paper adds.

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Despite the FA Cup triumph, reports the Sun on Sunday, "United players have been frustrated by LVG's regimen and also believed he could go early next week".

Describing the relationship between manager and squad as a "loveless marriage, a couple who have stayed together for the sake of the kids", David Walsh in the Sunday Times says van Gaal has turned Manchester United into a "solid but ordinary side".

Saturday's 2-1 win against Crystal Palace at Wembley was "hardly the performance van Gaal would have been hoping for to convince supporters, let alone the United board, that he is worth another season at Old Trafford", writes Paul Wilson in the Observer.

"Rumours were rife on Saturday that Jose Mourinho would be appointed as van Gaal's successor in a matter of days," says Oliver Holt in the Mail on Sunday. But he cautions: "Whether he is the answer or not is a moot point but it has got to the stage where change is needed to jolt the club out of stasis."

The Sunday Telegraph notes Jesse Lingard's extra-time strike to win the Cup for United "ensured van Gaal maintains his proud record of having won at least one trophy for every club he has managed".